There are at least two distinct eras in Bluegrass flatpick history, and sub-eras within them. Doing some listening on YouTube will help someone newly attracted to this wonderfully melodic and rhythmic component of both Bluegrass and Swing music find what appeals to them the most (even though that is likely to change in time, and with more exposure to it).
The following two links present a great counterpoint in more ways than one. First is the one player who did more to bring Bluegrass guitar flatpicking to the forefront than anyone. He was (and is) literally the Father of Bluegrass flatpick guitar, Doc Watson. The second is (arguably of course) the current state of the art in the genre, David Grier.
They both perform the old fiddle tune standard "Black Mountain Rag". Doc is backed up by another guitarist is his video from 1991. David plays solo in 2010. Not the best work either of them has done, but an excellent comparison of two greats, two completely different styles, and two different eras.
I've been inspired, think I'll get my rig out of it's case and pick a bit :)